The pole-zero analysis portion of WRspice computes the poles and/or zeros in the small-signal ac transfer function. The program first computes the dc operating point and then determines the linearized, small-signal models for all the nonlinear devices in the circuit. This circuit is then used to find the poles and zeros.
Two types of transfer functions are allowed: one of the form (output voltage)/(input voltage) and the other of the form (output voltage)/(input current). These two types of transfer functions cover all the cases and one can find the poles/zeros of functions like input/output impedance and voltage gain. The input and output ports are specified as two pairs of nodes.
The pole-zero analysis works with resistors, capacitors, inductors, linear controlled sources, independent sources, BJTs, MOSFETs, JFETs and diodes. Transmission lines and Josephson junctions are not supported.
The keyword cur stands for a transfer function of the type (output voltage)/(input current) while vol stands for a transfer function of the type (output voltage)/(input voltage). The keyword pol stands for pole analysis only, zer for zero analysis only and pz for both. This feature is provided mainly because if there is a nonconvergence in finding poles or zeros, then, at least the other can be found. Finally, node1 and node2 are the two input nodes and node3 and node4 are the two output nodes. Thus, there is complete freedom regarding the output and input ports and the type of transfer function.
In interactive mode, the pz command, which takes the same arguments as the .pz line, can be used to initiate pole-zero analysis.
Pole-zero analysis is not available if Josephson junctions are included in the circuit.